414 cxxxix. DioscoREACE^. (baker). [Dioscovea. 



Order CXXXIX. DIOSCOREACEiE. (By J. G. Baker.) 



Flowers regular, usually dioecious. Male flowers : Perianth cam- 

 panulate; tube very short; segments 6, biseriate. Stamens inserted at 

 the base of perianth, 6 all perfect or 3 reduced to staminodia ; filaments 

 short; anthers 2-celled, dehiscing longitudinally; pistil rudimentary. 

 Female perianth cut down to the ovary. Staminodia usually present. 

 Ovary inferior, 3 -celled ; ovules 2 in a cell, superposed ; styles 3, very 

 short, stigmatose at the apex. Fruit capsular, rarely baccate. Seeds 

 usually flattened and winged ; albumen fleshy or cartilaginous ; embryo 

 minute. — Rootstock large and tuberous. Stems usually twining, some- 

 times prickly. Leaves simple or compound, with reticulated venation. 

 Flowers small, greenish, usually spicate. 



Species about 160, spread through the warmer zones of both liemispheres. 



1. DIOSCOREA, Linn. ; Benth. et Hook. f. Gen. PI. iii. 742. 



Flowers dioecious. Male perianth with- a very short tube and 6 

 subequal biseriate segments. Stamens 6 all perfect or 3 reduced to 

 staminodia, shorter than the perianth. Pistil rudimentary. Female 

 flowers with a similar perianth, 3 short styles and an oblong triquetrous 

 ovary. Capsule rigid, deeply 3-lobed, in the subgenus Eudioscorea 

 broader than long, with orbicular seeds winged all round the nucleus, 

 and in the subgenus Helmia oblong with the wing of the seed only 

 produced on the lower side of the nucleus. — Rootstock large and 

 tuberous. Stem twining. Leaves distinctly petiolate, opposite or 

 alternate, simple or compound, often with bulbils in their axils. 

 Flowers small, arranged in dense or lax spikes or racemes, solitary or 

 fascicled, produced from leafy or leafless nodes. 



Species about 150, spread through the warmer zones of both hemispheres. 



Leaves simple, all alternate. 

 Leaves and flowers glabrous. 



Male spikes (or racemes) simple. 

 Leaves cordate- 



Perianth-sfigments linear . . . . 1. D. sativa. 



Perianth- s-igments acute . . . . 2. Z). Buehanani. 



Leaves sagittate 3. i>. sagittata. 



Male racemes with lower pedicels bearing 2-3 



flowers . . . . . . . 4. D. hylophila. 



Male spikes panicled 5. D. macroura. 



Leaves beneath and flowers hairy. 

 Spikes or racemes short. 



Leaves grey-pubescent beneath . . . 6. I>. Mrtifiora. 



Leaves ferrugineo-tomentose beneath . . 7. D. ruhiginosa. 



Spikes or racemes very long . . . . 8. Z>. Preussii. 



Leaves simple, usually opposite. 

 Stem quadrangular, 4-winged. 



Flowers glabrous . . . . . . 9. -D. alata. 



Flowers tomentose 10. i>. colocasicBfolia. 



